Displays with minimized border regions having an apertured TFT layer for signal conductors

ABSTRACT

An electronic device may be provided with a display having a thin-film transistor layer. One or more holes in the thin-film transistor layer may be used to form pathways from display circuitry to other circuitry underneath the display. One or more conductive bridges may pass through holes in the thin-film transistor layer and may have one end that couples to the display circuitry and a second end that couples to a printed circuit underneath the display. These conductive bridges may be formed from wire bonding. Wire bond connections may be encapsulated with potting material to improve the reliability of the wire bond and increase the resiliency of the display. Display signal lines may be routed through holes in a thin-film transistor layer to run along a backside of the display thereby reducing the need for space in the border region for display circuitry.

BACKGROUND

This relates generally to electronic devices and, more particularly, todisplays for electronic devices.

Electronic devices such as cellular telephones, computers, and mediaplayers are often provided with displays for displaying images to auser. Displays generally include multiple layers. For example, a displaymay include a layer of liquid crystal material sandwiched between twolayers of glass. Other types of displays such as flexible displays maycontain a layer of light-emitting material such as organiclight-emitting diodes (OLEDs) formed on a layer of flexible material. Adisplay may also include a display circuitry layer such as a thin-filmtransistor (TFT) layer that may be used to control the emission of lightin the display.

A flexible printed circuit (“flex circuit”) is often mounted to the TFTlayer in order to electrically connect the display circuitry to internalcomponents within the electronic device. A conductive adhesive is oftenused to mount the flexible circuit board to the TFT layer.

Conductive structures within a display and conductive structuresconnected to the display do not emit light and may therefore be locatedin the inactive region of a display. Additional border area may berequired for mounting a flex circuit to the TFT layer. Conductivestructures in the display border region and flex circuits attached tothe display border region may therefore reduce the amount of activedisplay area that is available to display images and may createaesthetically unappealing border regions around the periphery of thedisplay.

It would therefore be desirable to provide improved displays forelectronic devices.

SUMMARY

A display may be provided for an electronic device such as a portableelectronic device. A display may have an inner portion of active displayarea surrounded by a peripheral border of inactive display area.

A display may have a thin-film transistor (TFT) layer that containsdisplay circuitry for operating the display. A display may be providedwith one or more openings formed in the TFT layer in order to allowconductive bridges to pass through layers of the display. Conductivebridges may be formed from wire bonds or other conductive materials thatpass through the openings in the thin-film transistor layer connectingthe display circuitry with other device circuitry.

Wire bonds may form conductive bridges that pass down through theopenings in the TFT layer. Wire bonds that pass through the openings mayhave one end coupled to an electrical contact on the surface of the TFTlayer and another end coupled to an electrical contact on the surface ofother device circuitry.

Potting may be formed over the wire bonds to improve the reliability ofthe wire bonds.

Openings in the TFT layer may be filled with a conductive material. Theconductive material may have a portion that is electrically coupled toan electrical contact associated with the TFT layer and another portionthat is electrically coupled to an electrical contact associated withother device circuitry. One or more wire bonds or flex circuits may beused to electrically connect the display circuitry with the conductivematerial in the opening.

Further features of the invention, its nature and various advantageswill be more apparent from the accompanying drawings and the followingdetailed description of the preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an illustrative electronic device suchas a handheld electronic device with a display in accordance with anembodiment of the present invention.

FIG. 2 is a cross-sectional side view of a conventional electronicdevice having display circuitry arrangements that result in undesirablylarge inactive display areas around the border of a display.

FIG. 3 is a cross-sectional side view of a portion of an illustrativeelectronic device having conductive bridges that pass through holes inthe thin-film transistor layer of a display in accordance with anembodiment of the present invention.

FIG. 4 is a cross-sectional side view of a portion of an illustrativeelectronic device having wire bonds that pass through a gap between thedisplay and an enclosure in accordance with an embodiment of the presentinvention.

FIG. 5 is a cross-sectional side view of a portion of an illustrativeelectronic device having potting that is used to improve the reliabilityof wire bonds in accordance with an embodiment of the present invention.

FIG. 6 is a cross-sectional side view of a portion of an illustrativeelectronic device having openings in the thin-film transistor layer of adisplay that are filled with a conductive material coupled to wire bondsin accordance with an embodiment of the present invention.

FIG. 7 is a cross-sectional side view of a portion of illustrativeelectronic device having openings in the thin-film transistor layer of adisplay that are filled with a conductive material coupled to a flexcircuit in accordance with an embodiment of the present invention.

FIG. 8 is a top view of a conventional display having a displaycircuitry arrangement that results in undesirably large inactive displayareas around the border of a display.

FIG. 9 is a top view of an illustrative display having holes formed inthe thin-film transistor layer in accordance with an embodiment of thepresent invention.

FIG. 10 is a perspective view of an illustrative display having roundholes formed throughout the thin-film transistor layer in accordancewith an embodiment of the present invention.

FIG. 11 is a perspective view of an illustrative display havingrectilinear holes formed throughout the thin-film transistor layer inaccordance with an embodiment of the present invention.

FIG. 12 is a cross-sectional side view of a portion of illustrativeelectronic device having wire bonds that pass through openings in thethin-film transistor layer of a display in accordance with an embodimentof the present invention.

DETAILED DESCRIPTION

An electronic device may be provided with a display. Displays may beused to display visual information such as text and images to users.

An illustrative electronic device of the type that may be provided witha display is shown in FIG. 1. Electronic device 10 may be a portableelectronic device or other suitable electronic device. For example,electronic device 10 may be a laptop computer, a tablet computer, asomewhat smaller device such as a wrist-watch device, pendant device, orother wearable or miniature device, a cellular telephone, media player,electronic book, etc. The electronic device might be a larger device aswell, such as a television or digital sign.

Device 10 may include a housing such as housing 12. Housing 12, whichmay sometimes be referred to as a case, may be formed of plastic, glass,ceramics, fiber composites, metal (e.g., stainless steel, aluminum,etc.), other suitable materials, or a combination of these materials. Insome situations, parts of housing 12 may be formed from dielectric orother low-conductivity material. In other situations, housing 12 or atleast some of the structures that make up housing 12 may be formed frommetal elements.

Device 10 may have a display such as display 14. Display 14 may be rigidor flexible or may have a combination of rigid and flexible layers. Forexample, a flexible display may include an array of organiclight-emitting diodes (OLEDs) formed on a flexible substrate. For thepurpose of this invention, organic light-emitting diode displays areintended to encompass all types of light-emitting displays that comprisethin organic film layers, including displays comprising organic smallmolecules, polymers, dendrimers, and quantum dots. The thin film layerswithin the organic light-emitting display may comprise a cathode layer,an anode layer, one or more emissive layers, one or more hole transportlayers, one or more electronic transport layers, capping layers, holeinjection layers, electron injection layers, exciton blocking layers,and blends and composites of these materials. Other types of flexibledisplay technologies may be used to form a flexible display (e.g.,electronic ink displays, electronic paper displays, etc.).

As another example, a liquid crystal display (LCD) may include a layerof liquid crystal material sandwiched between two rigid substrates. Ingeneral, display 14 may be based on any suitable display technology(liquid crystals, light-emitting diodes, organic light-emitting diodes,plasma cells, electronic ink arrays, electronic paper displays, flexibleliquid crystal displays, flexible electrochromic displays, flexibleelectrowetting displays, etc.).

In some configurations, portions of display 14 such as peripheralregions 20I may be inactive and portions of display 14 such asrectangular central portion 20A (bounded by dashed line 20) maycorrespond to the active part of display 14. In active display region20A, an array of image pixels may be used to present text and images toa user of device 10. In active region 20A, display 14 may include touchsensitive components for input and interaction with a user of device 10.If desired, regions such as regions 20I and 20A in FIG. 1 may both beprovided with display pixels (e.g., all or substantially all of theentire front planar surface of a device such as device 10 may be coveredwith display pixels).

The width of peripheral regions 20I (sometimes referred to as the“peripheral border”) may be dictated by the amount of space neededwithin the display on which to form display circuitry or on which tomount connecting structures that connect the display components to otherdevice components. It may be desirable to minimize the width ofperipheral regions 20I in order to increase the active region of thedisplay and to create a more aesthetically appealing device.

Display 14 may be provided with openings in a display circuitry layersuch as a thin-film transistor layer that allow electrical connectionswith other device components to pass through the openings. Formingelectrical connections that pass through openings in a display layer mayhelp reduce the amount of circuitry formed in peripheral regions 20I ofdisplay 14 thereby reducing the required width of peripheral regions20I. Electrical connections that pass through openings in a displaylayer may include wire bonds or other conductive bridges through theopenings.

It may be aesthetically unappealing to have asymmetric border regions inthe display of an electronic device such as device 10. Circuitry thatincreases the width of peripheral border 20I on one side of display 14may therefore be matched by additional unused peripheral border 20I onanother side of display 14 to preserve display symmetry. Reducing thewidth of peripheral region 20I on one side of display 14 (e.g., bottomportion 24, sometimes referred to as the “bottom border”) may thereforereduce the width of peripheral regions 20I on another side of display 14(e.g., top portion 22).

A cross-sectional side view of a conventional electronic device in thevicinity of a bottom border of a display is shown in FIG. 2. Device 100includes display 200 and enclosure 38. Display 200 contains color filterlayer 200A and TFT layer 200B.

A flexible circuit is often used to electrically connect displaycircuitry with other circuitry within the device. Anisotropic conductivefilm 35 is used to mount one end of flex circuit 34 to the upper surfaceof TFT layer 200B. Conductive adhesive 35 forms an electrical connectionbetween flex circuit 34 and contact pad 540. Contact pad 540 istypically connected to one or more traces in the TFT layer such as trace19.

In a typical arrangement, flex circuit 34 wraps around one end of TFTlayer 200B by passing through gap 37 between TFT layer 200B andenclosure 38 and then curving back under TFT layer 200B. The end of flexcircuit 34 that is not connected to the TFT layer is connected withprinted circuit board 36.

Flex circuit 34 and other circuitry on TFT layer 200B does not emitlight and may therefore create an inactive display region such asinactive border 40. Inactive border 40 includes both the space needed onlayer 200B to mount flex circuit 34 as well as the width of gap 37between TFT layer 200B and enclosure 38 that is required to allow flexcircuit 34 to wrap around the end of TFT layer 200B.

The inactive portion of a display may be minimized by reducing theamount of space needed for display circuitry and by reducing the gapbetween the display and the enclosure. FIG. 3 is a cross-sectional sideview (i.e., a cross-section taken along axis 15 of FIG. 1) of anelectronic device of the type shown in FIG. 1 illustrating how theinactive bottom border of a display may be minimized by providingopenings in a display layer that allow conductive bridges through theopenings.

As shown in FIG. 3, device 10 may include a display such as display 14.Display 14 may have multiple layers such as display layer 14A andthin-film transistor (TFT) layer 14B. Display layer 14A may be a colorfilter layer that includes an array of colored filter elements. A layerof liquid crystal material such as liquid crystal layer 13 may beinterposed between color filter layer 14A and TFT layer 14B. This ismerely illustrative. If desired, display 14 may be an organiclight-emitting diode display that does not include a color filter layeror a liquid crystal layer. As another example, display 14 may be anorganic light-emitting diode display that includes a color filter layeror other color changing material. Display 14 may, in general, be basedon any suitable display technology (liquid crystals, organiclight-emitting diodes, plasma cells, electronic ink arrays, flexibleliquid crystal displays, electrochromic displays, electrowettingdisplays, etc.). Display 14 may be comprised of one or more glasssubstrates or substrates that include polymers or metal films. Ifdesired, display 14 may be a flexible display. Examples that use liquidcrystal technology are sometimes described herein as an example.

TFT layer 14B may include circuitry for operating display 14 such asdisplay driver circuitry and thin-film transistors. If desired, TFTlayer 14B may be a thin plastic film formed from polyimide, Polyethylenenaphthalate (PEN), Polyethylene terephthalate (PET), other suitablepolymers, a combination of these polymers, etc. Other suitablesubstrates that may be used to form TFT layer 14B include glass, metalfoil covered with a dielectric, a multi-layer polymer stack, a thinglass film bonded to a thin polymer, a polymer composite film comprisinga polymer material combined with nanoparticles or microparticlesdispersed therein, etc. For example, a layer of polyimide may be used toform the substrate for TFT layer 14B. TFT layer 14B may have a thicknessof 10-25 microns, 25-50 microns, 50-75 microns, 75-100 microns, 100-125microns, 125-150 microns, or more than 150 microns. In one particularexample, TFT layer 14B may be 100 microns thick.

Other layers or sublayers that may be included in display 14 include atouch-sensitive layer (e.g., a sheet of polymer with an array oftransparent capacitor electrodes for a capacitive touch sensor), opticallayers such as polarizing layers, shielding layers (e.g., for shieldingunwanted electric fields), heat sinking layers (e.g., for conductingheat away from the display), sealing layers (e.g., layers of sealantformed from thin films, polymers, inorganic materials, metal foils,composites, etc.), cover layers (e.g., a layer of cover glass), othersuitable display layers, or a combination of these display layers.

TFT layer 14B may include display circuitry such as display circuitry 53for operating display 14. Display circuitry 53 may include display imagepixel structures such as display electrodes and display circuitry forcontrolling the display electrodes. Display circuitry 53 may form aportion of an array of thin-film transistors (TFTs) that correspondswith an array of display image pixels. Display circuitry 53 may includetouch sensor electrodes, transistors (e.g., polycrystalline silicontransistors, amorphous silicon transistors, organic thin-filmtransistors, metal oxide transistors, carbon nanotube or graphenetransistors, other nanoparticle-based transistors, etc.), interconnectlines associated with a thin-film transistor array or other image pixelarray, integrated circuits, driver integrated circuits, other conductivestructures, or a combination of these conductive structures.

Circuitry 53 in TFT layer 14B may be interconnected using traces such asconductive trace 23. Conductive traces such as trace 23 may be coupledto one or more contact pads such as contact pad 54A. It may be desirableto connect display circuitry to other circuitry in the device (e.g., amain logic board or other printed circuit). One or more conductive pathssuch as conductive bridge 56 may be used to form an electricalconnection between traces such as trace 23 and other circuitry withinthe device such as printed circuit substrate 58. As shown in FIG. 3,conductive bridge 56 may pass through an opening in the display such asopening 50A in TFT layer 14B.

Printed circuit 58 and other printed circuits in device 10 may be formedfrom rigid printed circuit board material (e.g., fiberglass-filledepoxy), flexible sheets of material such as polymers, or a combinationof rigid and flexible materials (sometimes referred to as “rigid-flex”printed circuit boards). Flexible printed circuits (“flex circuits”)may, for example, be formed from flexible sheets of polyimide.

Conductive paths such as conductive bridges 56 that connect displaycircuitry with other circuitry in electronic device 10 may have one endthat bonds with a contact on the surface of the TFT layer and anotherend that bonds with a contact on the surface of a printed circuit withinthe device. In the example shown in FIG. 3, conductive bridge 56 mayhave one end that bonds with contact pad 54A (on the surface of TFTlayer 14B) and another end that bonds with contact pad 54B (on thesurface of printed circuit 58).

Conductive bridge 56 may be formed from aluminum, copper, gold, othermetals, other suitable conductive materials, a combination or compositeof conductive materials, etc. Portions of conductive bridge 56 mayinclude flex circuitry formed from flexible sheets of material such aspolymers. Conductive bridge 56 may, in general, be formed using anysuitable connector or mounting technology. In the example of FIG. 3,conductive bridge 56 is formed using one or more wire bonds that passthrough openings in the display such as opening 50A in TFT layer 14B.Wire bond 56 electrically couples bond pad 54A of TFT layer 14B withbond pad 54B of printed circuit 58. This is merely illustrative.Conductive bridge 56 may be formed from other types of conductiveconnectors. Wire bonding to form conductive bridges 56, as shown in FIG.3, is sometimes described herein as an example.

Wire bonds 56 may be formed from wedge bonding, ribbon wedge bonding(e.g., to create a flat ribbon wire), ball bonding, other suitable wirebonding methods, etc. The welding process used to form wire bonds 56 maybe facilitated with ultrasonic energy, thermal energy, pressure, or acombination of these forms of energy. Wire bonds 56 may have a diameterof 5-15 microns, 15-25 microns, 25-35 microns, 35-50 microns, or morethan 50 microns. For illustrative purposes, the wires used for bondingmay have a diameter of 25 microns, defining the minimum size of thecontacting area. Alternatively, wires of 32 micron diameter may be used.Materials that may be used in forming wire bonds 56 include TungstenCarbide, Titanium Carbide, composite materials (e.g., a compositematerial formed from ceramic and metal), other suitable materials,combinations of these materials, etc.

One or more openings such as opening 50A (sometimes referred to as ahole) may be formed in TFT layer 14B in order to allow conductivebridges such as conductive bridge 56 (sometimes referred to as a wirebond) to pass through TFT layer 14B and couple to other device circuitrythat is adjacent to the lower surface of TFT layer 14B such as printedcircuit 58 underneath display 14. Openings 50A may be designed tofacilitate a wire bonding process that uses a bonding tool to attachwire bond 56 to bond pads 54A and 54B (sometimes referred to as landingpads). Openings 50A may provide enough clearance around the edges ofbond pad 54B to allow the tool to connect to bond pad 54B. Bond pads maybe spaced sufficiently far apart to avoid shorting leads. Openings inthe TFT layer such as opening 50A may be formed using any suitablemethod (e.g., mechanical-drilling, laser-drilling, inserting a hotelement, etc.) and may have any suitable shape (circular, rectilinear,other suitable shape, etc.).

Display 14 may be enclosed on one or more ends by an enclosure such asenclosure 62. Enclosure 62 may be formed from part or all of one or morestructures in device 10. For example, enclosure 62 may be formed frompart of device housing 12. Providing openings 50A in TFT layer 14B thatallow conductive bridges 56 to pass through TFT layer 14B may allow agap between TFT layer 14B and enclosure 62 to be smaller than gapsbetween displays and device housings in conventional devices. Providingopenings 50A in TFT layer 14B that allow conductive bridges 56 to passthrough TFT layer 14B may reduce the border regions around display 14required for mounting connecting structures. Reducing the space neededin these areas may minimize the overall width of display border 60I(e.g., a bottom border of display 14), allowing for active display areasuch as active display region 60A to extend closer to the edge of device10 than in conventional devices.

FIG. 4 is a cross-sectional side view of a portion of device 10illustrating another example of how the inactive portion of a displaymay be minimized. In this example, conductive bridges may couple displaycircuitry with other device circuitry by passing through the gap betweenthe display and the display enclosure. As shown in FIG. 4, a gap such asgap 50B may be formed between TFT layer 14B and enclosure 62. Conductivebridges such as wire bond 56 may pass through opening 50B to couple tocircuitry underneath the display such as printed circuit 58.

Conductive bridge 56 may be a wire, a flat ribbon, a bundle of wires, ora bundle of flat ribbons formed using the method of wire bonding. Usinga wire bond such as wire bond 56 to couple display circuitry with otherdevice circuitry may allow a gap between TFT layer 14B and enclosure 62to be smaller than gaps between displays and device housings inconventional devices. Wire bond 56 may also reduce the peripheral areaaround display 14 required for mounting connecting circuitry. Reducingthe space needed in these areas may minimize the overall width ofdisplay border 64I (e.g., a bottom border of display 14), allowing foractive display area such as active display region 64A to extend closerto the edge of device 10 than in conventional devices.

It may be desirable to cover or encapsulate conductive bridge 56. FIG. 5is a cross-sectional side view of a portion of device 10 illustratinghow potting may be used to encapsulate wire bond 56. After forming wirebond 56, an encapsulant such as potting material 66 may be used to fillopening 50A and surround wire bond 56. Potting material 66 may alsosurround the junction between wire bond 56 and contact pad 54A, as wellas the junction between wire bond 56 and contact pad 54B. Examples ofmaterials that may be used in forming potting 66 include epoxy,silicone, urethane, acrylic, polyester, other types of potting material,a combination of these potting materials, etc.

Potting or encapsulating conductive bridge 56 may provide severalbenefits to both the conductive path itself and the electronic device.For example, in some configurations TFT layer 14B may be formed fromglass. A glass surface with multiple holes in it such as hole 50A may beprone to failure if exposed to excess pressure or force. Fillingopenings in TFT layer 14B such as opening 50A with potting material mayincrease the resiliency of the display around the openings. Otherbenefits of using potting material 66 may include protection againstmoisture, contaminants, and corrosion, electrical insulation, heatdissipation, and other benefits. Potting material 66 may also helpdivert unwanted pressure away from the display and improve thereliability and robustness of wire bonds 56.

Other features may optionally be added to improve the resiliency of thedisplay and the reliability of conductive bridges 56. For example, alayer of adhesive such as adhesive 68 may be formed between TFT layer14B and printed circuit 58. If desired, adhesive 68 may surroundopenings in TFT layer 14B such as opening 50A. Adhesive 68 may beconfigured to attach printed circuit substrate 58 to the underside ofTFT layer 14B. Adhesive 68 may increase the robustness of the displayaround these openings and may also provide protection against moisture,contaminants, and corrosion. Adhesive 68 may be formed from pressuresensitive adhesive (PSA), epoxy, or other suitable adhesives.

The space-saving benefits of using one or more holes in the TFT layerfor connections between display circuitry and other device circuitry maybe obtained with other configurations. One example of an alternativeconfiguration is shown in FIG. 6. In this example, opening 50A is filledwith a conductive material, such as conductive material 25. Conductivematerial 25 may be formed from conductive paste, conductive adhesive,conductive foam, or other suitable conductive material. An electricalcontact such as contact pad 54C may be situated over opening 50A on thesurface of conductive material 25. Contact pad 54C may be a separatecomponent from conductive material 25 or may be formed from anintegrated portion of conductive material 25. An additional electricalcontact such as contact pad 54D may be situated under opening 50A on thesurface of other device circuitry such as printed circuit substrate 58.Conductive material 25 may form an electrical connection betweenelectrical contacts 54C and 54D.

Conductive bridges such as wire bond 59 may be used to connect bond pad54A with conductive material 25. Wire bond 59 may have one end thatbonds with contact pad 54A (on the surface of TFT layer 14B) and anotherend that bonds with contact pad 54C (on the surface of conductivematerial 25). Signals may travel from display circuitry 53 to otherdevice circuitry 58 via wire bond 59 and conductive material 25.

If desired, other materials may be used to connect bond pad 54A withconductive material 25 inside opening 50A. For example, as shown in FIG.7, a layer of conductive adhesive such as conductive adhesive 49 may beused to mount a portion of a flexible circuit such as flex circuit 63over electrical contacts 54A and 54C. Conductive adhesive 49 may beformed from anisotropic conductive film (ACF) or other suitableconductive adhesive. Signals may travel from display circuitry 53 toother device circuitry 58 via flex circuit 63 and conductive material25.

Forming conductive bridges (e.g., wire bonds, conductive pastes, etc.)through holes in the TFT layer may provide a robust electrical bridgebetween display circuitry and other device circuitry while minimizinginactive display border regions.

It may be desirable to reduce the width of inactive display area aroundthe entire periphery of a display. In a conventional display such asdisplay 140 shown in FIG. 8, width 140W of inactive display border 140Iis typically dictated by display driver circuitry located in borderregion 200. Each row and column in a pixel array may have an associatedconductive trace (sometimes referred to as an interconnect, driver line,or control line). Typically, these traces will run alongside each otherin a common plane, parallel to side border 720 (i.e., parallel to they-axis shown in FIG. 8). This method requires an added amount of widthin region 200 of inactive display border 140I for each trace coming outof active display region 140A. Since each row and column of a pixelarray may have a control line associated with it, each added row orcolumn of pixels in a conventional display may increase the width (suchas width 140W) of inactive display border 140I.

FIG. 9 is a top view of display 14 illustrating how the width ofinactive display borders may be reduced by routing display control linesthrough openings in a TFT layer. As shown in FIG. 9, display 14 maycontain display circuitry such as driver integrated circuit 51 drivercircuitry 55. Driver integrated circuit 51 and driver circuitry 55 maybe used to drive signals to an array of pixels in display 14. Signallines such as signal lines 99 may be used to distribute signals from thedisplay driver circuitry to control lines such as control lines 41. Asshown in FIG. 9, control lines 41 may include data lines (D) and gatelines (G).

A plurality of holes such as holes 50C may be formed in one or morelayers of display 14 such as TFT layer 14B. Signal lines 99 may passthrough holes 50C in display 14 (parallel with the z-axis as marked inFIG. 9) to run along a back side of the display. If desired, signallines 99 coming from driver integrated circuit 51 may pass down throughholes 50C (in region 81A) to a printed circuit adjacent to the back sideof display 14 and may pass up through holes 50C (in region 81B) to reachcontrol lines 41. This may reduce the need for space in the borderregion for display circuitry.

As shown in FIG. 10, a plurality of holes such as holes 50C may beformed throughout TFT layer 14B. If desired, holes such as holes 50C maybe formed on one side, on two sides, on three sides, or on all foursides of display 14. Holes 50C may be located in regions of TFT layer14B that protrude out from under display layer 14A such as regions 81Aand 81B. Holes 50C may also be located in regions of TFT layer 14B thatare covered by display layer 14A. In general, holes may be locatedanywhere in TFT layer 14B.

Holes in the TFT layer may be of any suitable size or shape. Forexample, holes such as holes 50C of FIG. 11 may have a rectilinearshape.

Holes 50C of FIGS. 9-11 may be used to form a connection path fromdisplay circuitry to other device circuitry. Signal lines from displaycircuitry may be routed through openings 50C in the TFT layer to runalong a back side of the display. This may help reduce the width ofinactive display area around the border of a display. FIG. 12 is across-sectional side view (cross-section taken along axis 85 of FIG. 1)of device 10 in the vicinity of display 14 illustrating how holes suchas hole 50C (sometimes referred to as an opening) may help reduce width14W of inactive display border regions.

In the example shown in FIG. 12, display 14 may be a liquid crystaldisplay (LCD). Display 14 may have multiple layers such as color filterlayer 14A, TFT layer 14B, and light source layer 14C. A layer of liquidcrystal material such as liquid crystal 13 may be interposed betweencolor filter layer 14A and TFT layer 14B. Light source layer 14C may bea backlight layer that illuminates the liquid crystal material from theback of display 14.

Components on TFT layer 14B such as pixels 98 may be interconnectedusing traces such as conductive traces 41 (sometimes referred to ascontrol lines). Control lines 41 may be configured to control the arrayof pixels and may be connected to one or more electrical contacts on TFTlayer 14B such as contact pad 84A.

It may be desirable to route signal lines from display circuitry throughopenings in the display. In some configurations, display circuitry suchas driver integrated circuit 51 may be located on the TFT layer as shownin the example of FIG. 9. In the example shown in FIG. 12, driverintegrated circuit 51 may optionally be located on a printed circuitunder the display such as printed circuit 88 adjacent to light sourcelayer 14C. Control signals from driver integrated circuit 51 may beconveyed to control lines 41 through conductive bridges such asconductive bridge 82 that pass through openings 50C in TFT layer 14B.

Signal lines 99 may be used to distribute control signals from driverintegrated circuit 51 to conductive bridge 82. Conductive bridge 82 maybe used to convey these control signals from signal lines 99 to controllines 41. Printed circuit 88 may be formed from rigid printed circuitboard material (e.g., fiberglass-filled epoxy) or flexible sheets ofmaterial such as polymers.

Conductive paths that pass through openings in the TFT layer may haveone end that bonds with a contact on the surface of the TFT layer andanother end that bonds with a contact on the surface of a printedcircuit within the device. In the example shown in FIG. 12, a conductivebridge such as conductive bridge 82 may have one end that bonds withcontact pad 84A (on the surface of TFT layer 14B) and another end thatbonds with contact pad 84B (on the surface of printed circuit 88).

Conductive bridge 82 may be formed from aluminum, copper, gold, othermetals, other suitable conductive materials, a combination or compositeof conductive materials, etc. Portions of conductive bridge 82 mayinclude flex circuitry formed from flexible sheets of material such aspolymers. Conductive bridge 82 may, in general, be formed using anysuitable connector or mounting technology. In the example of FIG. 12,conductive bridge 82 is formed using one or more wire bonds that passthrough openings in the display such as opening 50C in TFT layer 14B.Wire bond 82 electrically couples bond pad 84A of TFT layer 14B withbond pad 84B of printed circuit 88. Wire bond 82 passes through openings50C in TFT layer 14B. This is merely illustrative. Conductive bridge 82may be formed from other types of conductive connectors. Wire bonding toform conductive bridges 82, as shown in FIG. 12, are sometimes describedas an example.

Wire bonds 82 may be formed from wedge bonding, ribbon wedge bonding(e.g., to create a flat ribbon wire), ball bonding, other suitable wirebonding methods, etc. The welding process used to form wire bonds 82 maybe facilitated with ultrasonic energy, thermal energy, pressure, or acombination of these forms of energy. Wire bonds 82 may have a diameterof 5-15 microns, 15-25 microns, 25-35 microns, 35-50 microns, or morethan 50 microns. For illustrative purposes, the wires used for bondingmay have a diameter of 25 microns, defining the minimum size of thecontacting area. Alternatively, wires of 32 micron diameter may be used.Materials that may be used in forming wire bonds 82 include TungstenCarbide, Titanium Carbide, composite materials (e.g., a compositematerial formed from ceramic and metal), other suitable materials,combinations of these materials, etc.

To improve the reliability of wire bonds 82, potting material 66 may beformed around wire bond 82 in opening 50C. Potting material 66 may alsosurround the junction between wire bond 82 and contact pad 84A, as wellas the junction between wire bond 82 and contact pad 84B.

One or more openings such as opening 50C (sometimes referred to as ahole) may be formed in TFT layer 14B in order to allow conductivebridges such as conductive bridge 82 (sometimes referred to as a wirebond) to pass through TFT layer 14B and couple to printed circuit 88underneath display 14. Openings in the TFT layer such as opening 50C maybe formed using any suitable method (e.g., mechanical-drilling,laser-drilling, inserting a hot element, etc.) and may have any suitableshape (circular, rectilinear, other suitable shape, etc.).

By having conductive bridges such as wire bond 82 pass down throughholes in the display layers (parallel to the z-axis marked in FIG. 12)instead of running alongside each other in a single layer (parallel tothe y-axis marked in FIG. 12), the width of inactive display area (suchas width 14W) around the border of the display may be significantlysmaller than that of a conventional display. By positioning printedcircuit 88 underneath light source layer 14C, signal lines such assignal lines 99 that distribute signals to control lines 41 may belocated under an active portion of a display.

The foregoing is merely illustrative of the principles of this inventionand various modifications can be made by those skilled in the artwithout departing from the scope and spirit of the invention.

What is claimed is:
 1. An electronic device, comprising: a printedcircuit substrate; a thin-film transistor layer having an upper surfaceand having thin-film transistor circuitry on the upper surface thatcontrols display pixels of different colors, wherein the thin-filmtransistor layer includes an array of openings, wherein the thin-filmtransistor layer forms part of a display for the electronic devicehaving a layer of liquid crystal material, and wherein the thin-filmtransistor layer extends around an entire perimeter of each of theopenings; conductive structures that each pass through a respective oneof the openings in the thin-film transistor layer, wherein theconductive structures electrically couple the thin-film transistorcircuitry to circuitry on the printed circuit substrate; and a backlightlayer interposed between the printed circuit substrate and the thin-filmtransistor layer, wherein the backlight layer illuminates the layer ofliquid crystal material.
 2. The electronic device defined in claim 1wherein the conductive structures each comprise a wire bond that passesthrough a respective one of the openings in the thin-film transistorlayer.
 3. The electronic device defined in claim 2 wherein each of thewire bonds has a first end that is electrically connected to a bond padon the thin-film transistor layer and a second end that is electricallyconnected to a bond pad on the printed circuit substrate.
 4. Theelectronic device defined in claim 2 further comprising: pottingmaterial that fills each of the respective openings in the thin-filmtransistor layer and that encapsulates each of the wire bonds thatpasses through each of the respective openings.
 5. The electronic devicedefined in claim 2 wherein each of the wire bonds has a first end thatis electrically connected to a bond pad on the upper surface of thethin-film transistor layer and has a second end that is electricallyconnected to a bond pad on the printed circuit substrate.
 6. Theelectronic device defined in claim 5 wherein the display comprises acolor filter layer, and wherein the layer of liquid crystal material isinterposed between the color filter layer and the thin-film transistorlayer.
 7. The electronic device defined in claim 2 wherein the thin-filmtransistor layer comprises a flexible substrate that includes at leastone sheet of polymer.
 8. The electronic device defined in claim 2wherein the thin-film transistor layer comprises a flexible substratethat includes a metal foil.
 9. The electronic device defined in claim 1wherein the printed circuit substrate comprises a flexible printedcircuit substrate.
 10. The electronic device defined in claim 1, furthercomprising: a color filter layer that overlaps the thin-film transistorlayer to form the display pixels of different colors; and a plurality ofadditional openings in the thin-film transistor layer, wherein theplurality of additional openings overlap the thin-film transistor layer,the color filter layer, and the display pixels of different colors. 11.The electronic device defined in claim 1, wherein the display pixels ofdifferent colors are arranged in an array, and wherein the backlightlayer, the printed circuit substrate, and the array of display pixels ofdifferent colors each overlap each other.
 12. The electronic devicedefined in claim 11, wherein the printed circuit substrate has an uppersurface and a lower surface, and wherein the upper surface is interposedbetween the backlight layer and the lower surface, the electronic devicefurther comprising: a driver integrated circuit mounted to the lowersurface of the printed circuit substrate, wherein the driver integratedcircuit provides control signals to the thin-film transistor circuitrythrough the conductive structures that each pass through a respectiveone of the openings.
 13. The electronic device defined in claim 12,wherein the backlight layer, the printed circuit substrate, the array ofdisplay pixels of different colors, the layer of liquid crystalmaterial, and the driver integrated circuit each overlap each other. 14.The electronic device defined in claim 1, wherein the conductivestructures each comprise conductive material that fills a respective oneof the openings and that electrically couples the thin-film transistorcircuitry to the circuitry on the printed circuit substrate.
 15. Anelectronic device, comprising: a thin-film transistor layer having athin-film transistor layer substrate with opposing first and secondsurfaces, wherein an array of display pixels of different colors areformed on the first surface, wherein control lines are formed on thefirst surface that are configured to control the display pixels, whereinthe thin-film transistor layer substrate has a plurality of openings,and wherein each of the plurality of openings extends from the firstsurface to the second surface; and a printed circuit that extends behindthe thin-film transistor layer substrate such that the second surface isinterposed between the first surface and the printed circuit, whereinthe printed circuit contains signal lines that distribute controlsignals to the control lines through the plurality of openings, whereina given one of the signal lines passes from the first surface of thethin-film transistor layer substrate to the printed circuit through afirst opening in the plurality of openings, wherein the given one of thesignal lines extends behind the thin-film transistor layer substrate onthe printed circuit to a second opening in the plurality of openings,and wherein the given one of the signal lines passes from the printedcircuit to the first surface of the thin-film transistor layer throughthe second opening to couple the printed circuit to at least one of thecontrol lines.
 16. The electronic device defined in claim 15 furthercomprising conductive material that fills the openings, wherein thecontrol signals are conveyed through the conductive material.
 17. Theelectronic device defined in claim 15 further comprising wire bonds thatpass through the openings, wherein the control signals are conveyedthrough the wire bonds.
 18. The electronic device defined in claim 17,wherein each of the wire bonds passes through a respective opening inthe plurality of openings, the electronic device further comprisingpotting material that covers each of the wire bonds in each of therespective openings.
 19. The electronic device defined in claim 15further comprising a backlight layer interposed between the printedcircuit and the thin-film transistor layer, wherein the backlight layerilluminates the display pixels of different colors.
 20. The electronicdevice defined in claim 15 wherein the thin-film transistor layer formspart of a liquid crystal display, wherein the liquid crystal displaycomprises a color filter layer, and wherein the liquid crystal displaycomprises a layer of liquid crystal material interposed between thecolor filter layer and the thin-film transistor layer.
 21. Theelectronic device defined in claim 15 wherein the display pixelscomprise thin-film transistors and wherein the control lines includedata lines and gate lines.
 22. The electronic device defined in claim 15further comprising: a driver integrated circuit mounted on the printedcircuit behind the thin-film transistor layer substrate, wherein thegiven one of the signal lines couples the driver integrated circuit tothe at least one of the control lines through the at least one of theplurality of openings.
 23. The electronic device defined in claim 22,wherein the printed circuit has upper and lower surfaces, wherein theupper surface is interposed between the lower surface and the secondsurface of the thin-film transistor layer substrate, and wherein thedriver integrated circuit is mounted to the lower surface of the printedcircuit.
 24. The electronic device defined in claim 23, wherein thearray of display pixels of different colors overlaps the driverintegrated circuit.
 25. The electronic device defined in claim 15,further comprising: a driver integrated circuit mounted on the firstsurface of the thin-film transistor layer substrate, wherein the atleast one of the signal lines is coupled to the driver integratedcircuit on the first surface and extends on the first surface from thedriver integrated circuit to the first opening.
 26. The electronicdevice defined in claim 25, wherein the control lines comprise gatelines and data lines, wherein the at least one of the signal linescouples the driver integrated circuit to the gate lines such that thedriver integrated circuit provides control signals to the gate linesthrough the first and second openings, and wherein the display driverintegrated circuit provides additional control signals to the data linesthrough conductive traces that are formed only on the first surface ofthe thin-film transistor layer substrate.